1. Technical Field of the Invention
The present invention relates to methods of manufacturing stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of the Related Art
Conventionally, there are known stators for electric rotating machines which include a hollow cylindrical stator core and a stator coil.
The stator core has a plurality of slots that are formed in the radially inner surface of the stator core and spaced in the circumferential direction of the stator core. The stator coil is comprised of a plurality of electric wires mounted on the stator core. Each of the electric wires includes a plurality of in-slot portions, each of which is received in a corresponding one of the slots of the stator core, and a plurality of turn portions each of which connects an adjacent pair of the in-slot portions and is located outside the slots of the stator core.
Moreover, as disclosed, for example, in Japanese Patent Application Publication No. 2009-247199, the stator coil may be formed by: (1) assembling the electric wires to form a planar electric wire assembly; and (2) rolling the planar electric wire assembly by a predetermined number of turns into a hollow cylindrical shape.
For the thus-formed stator coil, it is necessary for corresponding in-slot portions of the electric wires which are to be received in the same slot of the stator core to be aligned in a radial direction of the stator coil. However, due to springback of the electric wires, it may be easy for misalignment between the corresponding in-slot portions of the electric wires to occur during the rolling step.
The misalignment may make it difficult to accurately assemble the stator coil with the stator core. Further, the misalignment may also decrease the space factor of the corresponding in-slot portions of the electric wires in the slot of the stator core and deteriorate the magnetic characteristics of the stator.
Specifically, as shown in FIG. 35, the corresponding in-slot portions of the electric wires may be deviated from each other in the circumferential direction of the stator coil (or in the circumferential direction of the stator core), resulting in the misalignment between the corresponding in-slot portions in the radial direction of the stator coil (or in the radial direction of the stator core).
Moreover, as shown in FIG. 36, the corresponding in-slot portions of the electric wires may be twisted to become non-parallel to each other. In this case, a corner portion of one of the corresponding in-slot portions may come into contact with a radial end face of another one of the same, thereby damaging an insulating coat formed at the radial end face.
Furthermore, due to springback of the electric wires, the radially-innermost turn portions of the electric wires may protrude radially inward, causing interference between the stator coil and a rotor of the electric rotating machine which is disposed radially inside the stator. On the other hand, the radially-outermost turn portions of the electric wires may protrude radially outward, resulting in an increase in the outside diameter of the stator coil.